Method for coating of biaxially oriented film



Aug. 9, 1966 J. BERGGREN ET AL 3,265,552

METHOD FOR COATING OF BIAXIALLY ORIENTED FILM Original Filed Nov. 24.1961 5 Sheets-Sheet 1 LORING J. BERGGREN INVENTORS. CHARLES T HATHAWAYMM(Y.%MM

TTORNEY.

Aug. 9, 1966 ERGGRE ET AL 3,265,552

METHOD FOR COATING OF BIAXIALLY ORIENTED FILM Original Filed Nov. 24,1961 5 Sheets-Sheet 2 in O fee ea\f [ll 1.0mm; J. BERGGRENQ INVENTORS.

CHARLES T. HATHAWAY 9, 1966 J. BERGGREN ET AL 3,265,552

METHOD FOR COATING OF BIAXIALLY ORIENTED FILM Original Filed Nov. 24.1961 5 Sheets-Sheet 4' JJ'g. ZIZ'- LORING J. BERGGREN INVENTORS.

CHARLES T. HATHAWAY 0 BY MIM- TORNEY.

Aug. 9, 1966 L. J. BERGGREN ETAL 3,265,552

METHOD FOR COATING OF BIAXIALLY ORIENTED FILM Original Filed Nov. 24.1961 5 Sheets-Sheet 5 LORING J. BERGGREN CHARLES T. HATHAWAY ATTORNEY IN VENTORS 3,265,552 METHOD FOR (IOATING OF BIAXIALLY ORIENTED FILMLoring J. Berggren, Wilbraham, Mass., and Charles T.

Hathaway, Covina, Calif., assignors to Monsanto Company, a corporationof Delaware Original application Nov. 24, 1961, Ser. No. 154,453 nowPatent No. 3,160,917, dated Dec. 15, 1964. Divided and this applicationAug. 12, 1964, Ser. No. 389,022

7 Claims. (Cl. 156-244) The present invention is directed to coatingfilms and sheets constituted of thermoplastic synthetic polymericmaterial, and more particularly, to coating films biaxially oriented bytubular processes.

This application is a division of copending application S.N. 154,453filed Nov. 24, 1961, now Patent No. 3,160,917.

It is generally known that polymer film can be advantageously modifiedfor many end uses by applying a coating to the film. Typical of the manyadvantages to be gained would be coatings adapted to provide barriersagainst air, moisture, abrasion, etc. Another important use has beendeveloped for polymer films having poor heat sealability such as, e.-g.,oriented polystyrene. Acrylic and vinyl acetate based coatings have beenfound to provide excellent heat-sealing properties to films thatpreviously shriveled or decomposed upon the application of heat. 7

In the past, polymer films were generally coated as a separate operationby dipping techniques, rollers, sprays and similar devices which tendedto greatly increase the cost of coated polymer films. In particular, thetemperature of biaxially oriented polymer films had to be maintained lowduring the coating and drying operations to prevent loss of orientation.These low temperature operations generally restricted the type ofcoating materials to those that were liquid at low temperatures and/orextended the drying cycle when solvents were used.

Accordingly, it is a primary object of this invention to provide aprocess by which to coat biaxial oriented films constituted ofthermoplastic synthetic polymeric material.

Another object is to provide films of biaxially oriented polymericmaterials exhibiting enhanced properties, the result of their havingbeen coated immediately after orientation.

Other objects of the invention will in part be obvious and will in partappear hereinafter.

These and'other objects of the present invention can be obtained by amethod designed first to introduce biaxial orientation into atubularly-shaped member of thermoplastic synthetic polymeric materialand secondly to introduce a uniform coating onto the inner surface ofthe oriented tubing.

The following drawings are provided for the purpose of illustratingvarious embodiments of the present invention:

FIGURE I is a side elevation in section and with parts brokenschematically illustrating apparatus which may be employed in thepresent invention;

FIGURE II is a partial rear elevation with parts broken schematicallyillustrating the same embodiment of the invention illustrated in FIGURE1;

FIGURE III is a schematic representation in section and with partsbroken particularly illustrating a mandrel and die head combinationwhich can be used in practice of the present invention;

FIGURE IV is a schematic representation in section and with parts brokenshowing the mandrel described in FIGURE II with cooling means;

United States Patent "ice broken showing the mandrel described in FIGUREIII with laminating means.

Referring to the drawings wherein like numbers refer to like partsthroughout, and first to FIGURES I-III, a biaxial orientation andcoating apparatus 10 is shown in conjunction with a tubular member 12 ofsynthetic polymeric material, the latter designed to be biaxiallyoriented and coated while being advanced over the former.

Specifically an extruder head 14, the remainder of the extruder notbeing shown, is shown having an annular die orifice 16, defined betweena die head casing 18 and die core 20, through which to extrude tubularmember 12. Thereafter, tubular member 12 is caused to be drawn over theexterior of mandrel 22.

Mandrell 22 is shown stationed above, and in axial alignment with thesaid die orifice 16 and is provided externally with an effectivelongitudinally diverging advance end 24 terminating in the advancedirection in stationing projection 26. The effect obtained on thediverging advance end 24 then is that of a truncated cone. The divergingadvance end 24 of mandrel 22 is further provided externally withcontinuous curvature when considered in cross-section. In this regard,the curvature preferably contributes a peripheral outline or profiledefining a circle, but it can also define various other ellipticalshapes.

The advance end 24 provides the situs where orientation, bothlongitudinal and lateral of tube 12, takes place. The after cylindricalsection 28 of mandrel 22, which is contiguous to or a rearward extensionof the previouslydescribed advance end 24, is by comparison of constantdiameter and serves a dual-fold purpose as a situs for coating the innersurface of tubular member 12 and as a situs where the biaxialorientation once initiated is permanentized by chilling or cooling oftubular member 12.

The fluid coating distributing means comprising a fluid coating feedsystem and an annular discharge orifice or groove for coating the innersurface of the tubular member is designed for wide application intubular biaxial orientation systems employing rigidly constructedmandrels. As shown in FIGURE III, the fluid coating material enters thefluid coating distributing means through feed pipe 30 under a lowpressure and passes into the manifold 32. A plurality of manifold exittubes 34 conduct the fluid coating material to the annular dischargeorifice 36 located around the periphery of the cylindrical section 28.

The cylindrical section 28 as shown in FIGURE III is designed such thatthe diameter of the mandrel defining the leaving peripheral surface 38located immediately above the annular groove 36 is reduced to permitpassage of the now coated polymer tube 12. The peripheral clearancebetween the leaving peripheral surface 38 and the tubular member 12, ineflect, controls the thickness of the coating applied to the polymertube 12. The coating fluid enters the fluid coating distributing meansunder slight pressure. A slight pressure is desirable in order tomaintain constant fluid fillage throughout the fluid coatingdistribution means, particularly within the annular discharge orifice 36as variations in fluid pressure within the annular discharge orifice 36will cause uneven deposits -of the coating material on the polymer tube12. However, changes in the magnitude of the pressure employed can serveto further control the thickness of the coating for any designatedperipheral clearance.

The coating fluid may be maintained under slight pressure by anysuitable means such as mechanical pumps, manometer legs, gravitysystems, gas pressure systems and similar devices. The pressurizingmeans shown in FIG- URE I, is a gravity system, comprising essentially acoating fluid reservoir tank 42 and a constant pressure outlet valve 44for maintaining a uniform pressure within the fluid coating distributingmeans. The fluid level Within the reservoir tank 42 is maintained bycontinuously replenishing fluid coating material from an externalsource, not shown, through pipe 46, It is usually desirable to utilize areservoir tank of large diameter to optimize fluid level control,thereby reducing possible pressure variations throughout the fluidcoating system. If desired, the temperature of the coating fluid may beincreased by externally heating the reservoir tank 42.

The mandrel should be provided with -a plurality of temperature controlZones. Different polymer materials will generally have different optimumorientation temperatures and the coating process is in some casesaffected by the temperature of the polymer film or the fluid coatingmaterial. Temperature control is therefore important. Themandrel shownmore clearly in FIGURE III is provided with a plurality of internaltemperature control zones. Heating zone 48 is located to the interior ofdiverging advance end 24. This expedient is designed to provide ormaintain and transfer that temperature to tubular member 12 at whichbiaxial orientation can be introduced into the same. Stand pipe 50,integrated to a source, not shown, serves to introduce heated fluid intoheating zone 48. The outer exhaust pipe 52 is installed for the purposeof making the heating fluid system of a continuous circulating nature.The secondary temperature control zone 54, located above, previouslydescribed heating zone 48, can be used to heat or cool the polymer filmto an optimum temperature consistent with both the film orientation andcoating operation. In order that the secondary temperature control zonecan be provided continuously with fluid for obtaining and maintainingthe desired temperature, supply pipe 56 and exhaust pipe 58, both ofwhich are connected to a source of fluid, are utilized.

In order to advance tube 12 at a predetermined speed over mandrel 22,take-off means are provided, which are shown in FIGURE II, taking theform of sheet bending and support rolls 60-60 and 62-62, and pairs ofpinch rolls 64-64, the pinch rolls being provided with a drive motor, orother source of power not shown.

Mandrel 22 is located intermediate, process-wise of annul-ar die orifice16, and the take-off means described immediately above. A film-slittingmeans, more particularly knives 6666, are shown located above mandrel 22in order that tube 12 upon leaving mandrel 22 can be slit into twoequi-width sheets and made available to be advanced through the variouscomponents of the take-off means in the form of two separatesingle-width sheets. This prevents creasing or film distortion whichwould otherwise occur if the film were directed through the takeoffmeans in tubular form. If greater sheet widths are desired, a singlefilm-slitting knife may be readily employed. In the preferredembodiment, tubular member 12 extends a few inches above (see FIGUREIII) the mandrel 22 before being cut by the film-slitting means. This isdone in order to maintain a uniform clearance be tween the inner surfaceof the polymer tube 12 and the leaving peripheral surface 38 of thecylindrical section 28 since this clearance is determinant of thethickness of the particular coating. A minimum separation of about twoinches between the mandrel 22 and the film-slitting means has been foundto be satisfactory.

For many coatings, particularly those carried in a solvent vehicle,drying means are necessary. In FIGURES I and II drying means areprovided in the form of air ducts 6868 positioned over the coatedsurfaces of the individual film halves. Temperature controlled air fordrying, from a source not shown, is forced through the perforatedunderportions 7070 of air ducts 68-68, respectively, for drying orcooling the coated surfaces of the polymer film.

FIGURE IV illustrates a third embodiment of the mandrel orientation andcoating apparatus which can be used in practice of the presentinvention. The mandrel 22 is the same as that previously described abovebut incorporates a hollow cooling ring 72 supported by means not shownlocated above the mandrel 22 and encompassing the outer surface of thetubular member 12 for cooling the tube after it advances above themandrel 22. In order that the hollow cooling ring can be providedcontinuously with fluid coolant of the desired temperature, intake pipe74 and exhaust pipe 76, both of which are connected to a source ofcoolant are utilized. The inner surface of the cooling ring 72, that is,that portion of said ring in contact with the outer surface of thetubular member 12 is polished to permit smooth passage of the polymertube 12 through the center opening of the cooling ring. The diameter ofthe cooling ring 72 may be varied, but preferably the diameter of thecenter opening of said cooling ring should be somewhat less than theouter diameter of the tubular member 12. The advantages of the coolingring are two-fold. First, the clearance between the tubular member 12and the leaving peripheral surface 38 of cylindrical section 28 can bevaried by moving the cooling ring up or down in relation to the mandrel22, thereby varying the thickness of the coating applied to the innersurface of the tubular member 12. Secondly and more importantly, thefluid coating material can be applied to the tubular member 12 at muchhigher temperatures without loss in biaxial orientation which otherwisecould occur if said tubular member were cut before it was cooled.Consequently higher melting and therefore less tacky coatings maybeutilized. In addition the increased temperature of the tubular member12 during advancement between the mandrel 22 and the cooling ring '72enhances the drying of solvent and aqueous coating systems which may befurther improved by increasing the distance between the mandrel and thecooling ring and/ or applying a low vacuum at this point. Film-slittingmeans, more particularly a pair of knives 78-78 are shown in FIGURE IVattached to and located above the cooling ring 72 in order that thetubular member 12 can be slit and made available to be advanced throughthe various components of the take-off means in the form of twosingle-width sheets. A single knife may be employed if a larger widthsheet is desired.

In brief, the present method for coating biaxial oriented tubular-shapedmembers of thermoplastic synthetic polymeric material comprises thesteps of (1) extruding a tubular member of thermoplastic syntheticpolymeric material, (2) laterally and longitudinally expanding saidtubular member by drawing said tubular member over and in contact with adiverging mandrel while maintaining the temperature of said tubularmember above its glassy transition temperature and (3) coating theinternal surface of said tubular member with a fluid coating.

The mandrel, which can be used in practice of the present invention, isof rigid construction so as to present a solid face or surface to thetubular member of thermoplastic material wherein -biaxial orientation isbeing introduced. The exterior shell of the mandrel which can be ofunitary or divisional construction can be fabricated from rigidmaterials such as various metals, alloys and ceramics, which have thecapacity for conducting heat, relatively uniformly and as adiabaticallyas possible, in order to contribute uniformity of orientation and,correspondingly, uniformity of physical properties and appearance in thefinal biaxially oriented film product. Materials particularlyrecommended for this are steel, copper, aluminum and various nickelalloys. The exterior surface should he polished in order to cut downfrictional forces between this surface and the interior of the tube offilm being advanced over the same.

As previously indicated, the advance end of the mandrel, that is theadvance end which serves as the situs for orientation, diverges in thedirection of advance, and has a continuous outside curvature incross-section. The after-part of the mandrel, which serves as the situsfor coating the film and permanentizing the orientation, once initiatedis generally of constant diameter, and again has a continuous outsidecurvature in cross-section.

The overall size of the mandrel in cross-section or circumference willdepend upon the internal circumference of the tubular member which isdesired to be attained with orientation (stretching) while thecircumference of the most advanced end can reflect the internal diameterof tubular member prior to introduction of orientation, which can bethat of the tubular member upon its being extruded from the die. Theangle of divergence on the advanced end can vary over wide limits,depending upon the amount of longitudinal or machine direction andlateral or transverse orientation which is intended to be introducedinto the tubular member. As previously mentioned, the type of coatingfluid utilized will vary dependent on the type of polymer film beingoriented and the purpose to be served. In illustration of the coatingoperation, a mandrel such as shown in FIGURE III, having a diameter of7.500 inches before the annular discharge orifice and a diameter of7.494 inches above said orifice; the Width of the annular dischargeorifice in the longitudinal direction of the mandrel being approximatelythree-fourths of an inch with a mid depth of approximately one-eighth ofan inch, and a taper angle for the mandrel advance end of 60 can be usedto orient and coat a tubular member of isotactic polystyrene having aStaudinger molecular weight of 5 5,000-70,000, an initial gauge of 40mil with an interior circumference of 4.7 inch and a final advance speedof 55 feet per minute. The coating fluid is comprised of 25 parts (byweight) of polyvinyl acetate dissolved in 75 parts (by weight) of ethylalcohol which is applied to the polystyrene surface to take advantage ofits peculiar moisture resistant and heat sealing properties. After thepolystyrene tube leaves the mandrel its guage (thickness) has beenreduced to 1 mil and it has an internal circumference of 23.5 inches,both in permanentized condition'with a coating thickness ofapproximately 0.0001 to 0.0002 inch. The resulting film when testedaccording to ASTM-Dl504 exhibits 200-600 p.s.i. orientation stress inthe machine direction and 100- 300 p.s.i. in the lateral. The force ofadhesion of the coating polystyrene surface heat-bonded at temperaturesof approximately 190 F. to 250 F. to the surface of an uncoated surfaceof polystyrene film is in the order of 5-10 pounds per square inch. Incarrying out this illustrative orientation and coating operation, thetemperature of the coating fluid is maintained at approximately 140 F.by varying the secondary temperature control zone within the range of60-175 F. while varying the heating zone between 225-245" F.

The location of the mandrel is such that the longitudinal axis of thesame is axially aligned with the axis of the die from which the tubularmember is being extruded. As indicated above, if the coating materialwere such as to require higher fluidizing temperatures, the orientationof the polystyrene film would be more advantageously permanentized by asubsequent cooling operation such as the cooling ring described above.

The present invention can also be utilized to apply coatings, as acenter layer, to films to produce a sandwich construction. FIGURE Villustrates a mandrel similar to that shown in FIGURE III which is usedin conjunction with laminating means. In this embodiment, a pair ofseparating rolls 8080 is employed to part the halves of the tubularmember 12 to permit piping access to the mandrel described in FIGUREIII. The tubular halves are then directed toward each other by a pair ofalignment rolls 82-82 and pressed together by the subsequently locatedlaminating r'olls 34-84 to form a continuous flat sandwich construction.Suppport rolls 86 and 38 and take rolls 90-90 convey the laminated sheetto a packout station not shown. In some cases lamination can be improvedby heating the laminating rolls 84-84 by utilizing pipes 92-92 tocirculate a heating medium through said laminating rolls. In thismanner, a film laminate having excellent moisture-proof properties canbe pro duced.

An illustration of a laminated product produced by this process would bea pair of polystyrene sheets having a central layer comprised of fiveparts (by weight) of a fatty acid amide in admixture with ninety-fiveparts (by weight) of paraffin wax.

The operation of the biaxial orientation apparatus in its most genericsense involves advancing the tubular member to 'be oriented, afterextrusion of the same, over a mandrel, Where it is first biaxiallyoriented and then coating the inner surface of the same while theorientation is permanentized by cooling. Thereafter the tubular memheris caused to be slit and formed into one or more single-width flatsheets, in which form they are either laminated or individually directedthrough take-off means to eventuate as laminates or individually coatedsheets of polymer film. Advance of the tubular member, and later thecoated flat sheet of synthetic thermoplastic material being biaxiallyoriented, as previously prescribed, is e-ffected by the take-off meanswhich includes one or more prime movers or driving means.

During operation of the presently sponsored apparatus, time andtemperature are important considerations. While these will varyaccording to the identity of the thermoplastic material being subjectedto orientation, the coating fluid to be applied, and in a lesser degree,the amount of orientation designed to be introduced, nevertheless is canbe broadly stated that orientation is introduced at a temperature aboveabout the glassy transition temperature T of the given thermoplasticmaterial while the coating fluid can be applied above or below saidglassy transition temperature. The orientation temperature will dependupon whether the material is of the noncrystallizable nature as in thecase of atactic polystyrene, low density polystyrene, polyvinylchloride, etc., or a crystallizable nature such as in the case ofisotactic polystyrene, linear polyethylene, polypropylene, etc. In allcases, the orientation step and the coating step should not be carriedout at a temperature which exceeds the melting point for the syntheticpolymer material being oriented and coated.

The permanentizing step, which is designed to stabilize orientation onceintroduced, is carried out at a temperature below the glassy transitiontemperature T and varies according to the synthetic plastic materialinvolved. Illustrative of this; polystyrene, polyethylene and polyvinylchloride undergo transitions in the temperature region T in theneighborhood of F. The coating operation can be carried out before orafter the permanentizing step depending on the melting point or optimumdrying temperatures for the coating material. If the melting point oroptimum drying temperatures of the coating material are above thetemperature required for permanentizing the orientation of the film, thecoating material would be applied before the permanentizing step. On theother hand, if the melting or drying point of the coating material is ator below the optimum permanentizing temperature range, the coatingoperation and permanentizing step can take place at the same time.

The sponsored method contributes a combined biaxial orientation surfacecoating operation which is simple in operation and serves to minimizetemperature control coating problems. Additionally, the simplicity ofthe method serves to reduce both operating cost and capital whencompared to other systems utilizing a separate and subsequent coatingoperation.

It Will thus be seen that the objects set forth above, among those madeapparent from the preceding description, are efiiciently attained and,since certain changes may be made in carrying out the above method andin the construction set forth without departing from the scope of theinvention, it is intended that all matter contained in the abovedescription shall be interpreted as illustrative and not in a limitingsense.

What is claimed is:

1. A method for coating biaxial oriented tubularshaped members ofthermoplastic synthetic polymeric material comprising the steps of (I)extruding a tubular member of thermoplastic synthetic polymericmaterial,

(2) laterally and longitudinally expanding said tubular 4 member bydrawing said tubular member over and in contact with a diverging mandrelwhile maintaining the temperature of said tubular member above itsglassy transition temperature and (3) coating the internal surface ofsaid tubular member with a fluid coating.

2. The method according to claim 1 wherein the thermoplastic syntheticpolymeric material is polystyrene.

3. The method according to claim 1 wherein the thermoplastic syntheticpolymeric material is linear polyethylene.

4. A method for coating biaxial oriented tubularshaped members ofthermoplastic synthetic polymeric material comprising the steps of (1)extruding a tubular member of thermoplastic synthetic polymericmaterial, (2) laterally and longitudinally expanding said tubular memberby drawing said tubular member over and in contact with a divergingmandrel while maintaining the temperature of said tubular member aboveits glassy transition temperature, (3) coating the internal surface ofsaid tubular member with a fluid coating and (4) cooling the tubularmember below its glassy transition temperature.

5. A method for coating biaxial oriented tubularshaped members ofthermoplastic synthetic polymeric material comprising the steps of (1)extruding a tubular member of thermoplastic synthetic polymericmaterial, (2) laterally and longitudinally expanding said tubular memberby drawing said tubular member over and in contact with a divergingmandrel while maintaining the temperature of said tubular member aboveits glassy transition temperature, (3) coating the internal surface ofsaid tubular member with a fluid coating, (4) cooling the tubular memberbelow its glassy transition temperature, (5) cutting the tubular memberinto two equal lengthwise halves and (6) pressing together the tubularhalves to form a continuous flat sandwich construction.

6. A method for coating biaxially oriented tubularshaped members ofthermoplastic synthetic polymeric material which comprises: (1) forminga tubular member of thermoplastic synthetic polymeric material; (2)drawing said tubular member at a temperature above its glassy transitiontemperature over and in contact with a diverging mandrel to laterallyand longitudinally expand said tubular member; (3) drawing the expandedtubular member over and in contact with a uniform cross-section1alextension of said mandrel to maintain the biaxial orientation of saidexpanded tubular member; (4) applying a fluid coating material betweensaid mandrel extension and said expanded tubular member to deposit acoating of said fluid material on the internal surface of said expandedtubular member; and (5) cooling the coated expanded tubular member to atemperature below the glassy transition temperature of saidthermoplastic synthetic polymeric material to permanentize the biaxialorientation of said tubular member.

7. The method of claim 6 wherein said fluid coating material is appliedunder pressure directed perpendicularly to the internal surface of saidexpanded tubular member.

References Cited by the Examiner UNITED STATES PATENTS 2,632,205 4/1953Fitz Harris 18 14 2,987,767 6/1961 Berry et a1. 1814 3,008,186 11/1961Voigt l8-14 3,074,108 1/1963 Wiley et 61. 18-14 3,108,324 10/1963Zavasnik l8-14 3,108,851 10/1963 Hofer et a1 18-14 3,159,698 12/1964 Suhet al. 264-210 EARL M. BERGERT, Primary Examiner.

M. L. KATZ, Assistant Examiner.

5. A METHOD FOR COATING BIAXIAL ORIENTED TUBULARSHAPED MEMBERS OFTHERMOPLASTIC SYNTHETIC POLYMERIC MATERIAL COMPRISING THE STEPS OF (1)EXTRUDING A TUBULAR MEMBER OF THERMOPLASTIC SYNTHETIFC POLYMERICMATERIAL, (2) LATERALLY AND LONGITUDINALLY EXPANDING SAID TUBULAR MEMBERBY DRAWING SAID TUBULAR MEMBER OVER AND IN CONTACT WITH A DIVERGINGMANDREL WHILE MAINTAINING THE TEMPERATURE OF SAID TUBULAR MEMBER ABOVEITS GLASSY TRANSSITION TEMPERATURE, (3) COATING THE INTERNAL SURFACE OFSAID TUBULAR MEMBER WITH A FLUID COATING, (4) COOLING THE TUBULAR MEMBERBELOW ITS GLASSY TRANSITION TEMPERATURE, (5) CUTTING THE TUBULAR MEMBERINTO TWO EQUAL LENGTHWISE HALVES AND (6) PRESSING TOGETHER THE TUBULARHALVES TO FORM A CONTINUOUS FLAT SANDWICH CONSTRUCTION;